All - Thank you all for the fantastic feedback. Tons of stuff to go through now!
Brent On Tue, Dec 28, 2021 at 1:54 PM Rob Seaman <[email protected]> wrote: > As Poul-Henning says, Polaris would be a poor choice, as would indeed any > stars or other objects fixed to the celestial sphere since their > differential motion is (very) slight. The issue isn’t measuring the rate, > but establishing a zero point, otherwise one day, indeed one year, is very > like the ones before or after. That said, spatial coordinates are > fundamentally tied to astronomical observations of quasars via very long > baseline interferometry. Space and time coordinates are intertwined ( > https://www.ivoa.net/documents/latest/STC.html < > https://www.ivoa.net/documents/latest/STC.html>), and precision > observations of pulsars can similarly be used to establish a long term > temporal baseline ( > https://www.iau.org/science/scientific_bodies/working_groups/304/ < > https://www.iau.org/science/scientific_bodies/working_groups/304/>). > > The solar system provides innumerable cycles for establishing absolute > time, whether sidereal (stellar) or synodic (solar) ( > http://hanksville.org/futureofutc/preprints/files/28_AAS_13-515_Seaman.pdf > < > http://hanksville.org/futureofutc/preprints/files/28_AAS_13-515_Seaman.pdf>). > Folks may be interested in other papers and presentations from this > workshop: http://hanksville.org/futureofutc/ < > http://hanksville.org/futureofutc/> (replace “www.cacr.caltech.edu < > http://www.cacr.caltech.edu/>” with “hanksville.org < > http://hanksville.org/>”, if you get redirected to the retired Caltech > server) and many of the transcribed discussions are interesting in their > own right ( > http://hanksville.org/futureofutc/preprints/files/29_AAS%2013-515discussion.pdf > < > http://hanksville.org/futureofutc/preprints/files/29_AAS%2013-515discussion.pdf>). > For many more topics pertaining to UTC and leap seconds, see > https://ucolick.org/~sla/leapsecs/ <https://ucolick.org/~sla/leapsecs/> > > An astronomer might quibble over the meaning of absolute time ( > https://galison.scholar.harvard.edu/publications/einsteins-clocks-poincarés-maps > < > https://galison.scholar.harvard.edu/publications/einsteins-clocks-poincar%C3%A9s-maps>). > Observations of Earth’s moon and of the Galilean moons of Jupiter were used > in the 18th Century as described in Dava Sobel’s excellent book “Longitude” > (http://www.davasobel.com/books-by-dava-sobel/longitude < > http://www.davasobel.com/books-by-dava-sobel/longitude>), along with some > more creative timekeeping attempts before Harrison #4. I presume most here > are familiar with Dumbledore’s role in the history of clocks ( > https://www.imdb.com/title/tt0192263/?ref_=nv_sr_srsg_2 < > https://www.imdb.com/title/tt0192263/?ref_=nv_sr_srsg_2>). Poul-Henning > mentions latitude and I’m not sure if this is what he meant or rather the > International Latitude Service ( > https://adsabs.harvard.edu/full/2000ASPC..208..147Y < > https://adsabs.harvard.edu/full/2000ASPC..208..147Y>), which is indeed an > interesting historical tale in its own right. > > One can use asteroid ephemerides as a clock ( > https://link.springer.com/chapter/10.1007/978-3-319-59909-0_36 < > https://link.springer.com/chapter/10.1007/978-3-319-59909-0_36>), though > the need for precision orbital elements fights the need for rapid motion. > Asteroid surveys detect (and redetect) tens of thousands of asteroids > nightly. Comparisons against their predicted positions can be summed to > arrive at fairly precise timing, eg, “this pattern of objects can only > correspond to one specific absolute time”. > > At the opposite end of the scale, the 10,000 Year Clock will use daily > solar observations (perhaps separated by decades due to waiting for sucker > holes in some post-apocalyptic death shroud of clouds) to keep within +/- 5 > minutes of mean solar time (https://arxiv.org/pdf/1112.3004.pdf < > https://arxiv.org/pdf/1112.3004.pdf>) …assuming humans don’t perturb the > Earth enough to make the Equation of Time Cam inaccurate ( > https://longnow.org/ideas/02018/12/05/the-equation-of-time-cam-keeping-good-time-for-10000-years/ > < > https://longnow.org/ideas/02018/12/05/the-equation-of-time-cam-keeping-good-time-for-10000-years/ > >). > > Observations of artificial satellites offer significantly more precision > since they are much closer to the observer, thus not only brighter and > easier to centroid, but move rapidly across the sky (though tracking rapid > objects is itself a challenge). The advent of satellite mega-constellations > in low Earth orbit will engender new infrastructure, including precision > ephemerides ( > https://www.space.com/sathub-idea-threat-satellite-megaconstellations-astonomy > < > https://www.space.com/sathub-idea-threat-satellite-megaconstellations-astonomy>) > that could be used for such. But, of course, the various GNSS > constellations already address this requirement ( > https://projectpluto.com/gps_expl.htm < > https://projectpluto.com/gps_expl.htm>). > > Greenwich Observatory played a fundamental role in the long history of > transmission of time signals ( > https://blog.sciencemuseum.org.uk/ruth-belville-the-greenwich-time-lady/ < > https://blog.sciencemuseum.org.uk/ruth-belville-the-greenwich-time-lady/>). > To those wondering in other threads whether such topics are appropriate for > Time-Nuts, I can only speak for myself that the engineering of large > systems of systems for conveying time signals most certainly does seem a > topic for this mailing list, whether via computer networks, cell phones, > radio signals from the ground or orbiting satellites, or indeed, carried in > a pocket, on our wrists, or in the back of an SUV ( > http://leapsecond.com/great2016a/ <http://leapsecond.com/great2016a/>). I > invite Tom back any time to our observatory to repeat his experiment! > > Rob Seaman > Lunar and Planetary Laboratory > University of Arizona > -- > > > On Dec 28, 2021, at 7:40 AM, Poul-Henning Kamp <[email protected]> > wrote: > > > > -------- > > Lux, Jim writes: > > > >> On 12/27/21 12:18 PM, Brent wrote: > >>> My understanding (and I could be wrong) is that one could derive > 'stellar' > >>> time from a start sight/fix on polaris or another well tracked > celestial > >>> object. I was once told that early editions of Bowditch provided the > >>> process (for the moon I was told) although one of the relatively old > >>> edition's that I have doesn't provide it. > > > > You want a bright star as close to your latitudes Zenith as possible, > > to get maximum apperant transit velocity. > > > > Polaris would be a spectacular bad choice as it barely moves at all. > > > >> Occultation of stars by the Moon provides a "universal" time source > >> (assuming you can see the Moon and stars). > > > > Interesting history search term: "Latitude observatory". > > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send > an email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
